While adolescents using e-cigarettes were more likely to be trying to quit, they were less likely to have stopped smoking and were smoking more, not less, the research found.

"We are witnessing the beginning of a new phase of the nicotine epidemic and a new route to nicotine addiction for kids," according to senior author Stanton A Glantz, from the University of California, San Francisco (UCSF).

E-cigarettes are battery-powered devices that look like cigarettes and deliver an aerosol of nicotine and other chemicals.

Promoted as safer alternatives to cigarettes and smoking cessation aids, e-cigarettes are rapidly gaining popularity among adults and youth in the US and around the world, researchers said.

The devices are largely unregulated, with no effective controls on marketing them to minors, they said. In the study, researchers assessed e-cigarette use among youth in Korea, analyzing smoking among some 75,000 Korean youth.

"Our paper raises serious concern about the effects of the Wild West marketing of e-cigarettes on youth," said Glantz.

The researchers reported that four out of five Korean adolescent e-cigarette users are "dual" smokers who use both tobacco and e-cigarettes.

They conclude that young e-cigarette smokers "are more likely to have tried quitting smoking, which suggests that, consistent with cigarette marketing messages, some youth may be using e-cigarettes as a smoking cessation aid."

"Use of e-cigarettes is associated with heavier use of conventional cigarettes, which raises the likelihood that actual use of e-cigarettes may increase harm by creating a new pathway for youth to become addicted to nicotine and by reducing the odds that an adolescent will stop smoking conventional cigarettes," researchers said.

Among students who used e-cigarettes, 8 percent were concurrently smoking conventional cigarettes. After adjusting for demographics, current cigarette smokers in the study were found to be much more likely to use e-cigarettes than non-smokers.

The researchers also found that the odds of using e-cigarettes were considerably higher among students who had made an attempt to quit smoking than those who had not.

Students no longer using cigarettes were rare among current e-cigarette users, the researchers said. The study appears in the Journal of Adolescent Health.